1. Field of the Invention
The present invention, generally, relates to apparatus for removing, replacing and attaching electronic components that are soldered in place on a printed wire board or substrate and, more particularly, to apparatus constructed to use a state changing medium having predetermined characteristics.
Typical rework stations available today to remove and to replace surface mounted components on a printed wire board or substrate are constructed to use (1) hot gas, (2) soldering tweezers, (3) hot plate (or hot belt) and (4) lasers. Rework stations using hot gas are the most popular. However, there are major problems with using hot gas, which include very high gas temperature to attain necessary thermal transfer, difficulty in controlling the time/temperature and difficulty in applying a hot gas selectively to only a component to be removed. Damage to a printed wire board or substrate is not uncommon, and with a densely packed surface mounted components and multiple layer printed wire boards today, the cost of such finished modules can easily run into many thousands of dollars.
In today's technology, a substrate includes much more than just a "printed circuit". It is a highly complex product of manufacture that includes interconnecting circuitry for miniaturized packages of electronic components fabricated as individual units, called "integrated circuits", which include usually a large number of solid state devices.
For dense packaging, it is the practice today to use printed wire boards bonded by adhesives to opposite sides of a metallic heat sink. Such structures increase exponentially the problems encountered when it becomes necessary to repair or to replace an integrated circuit component package, such as a leadless chip carrier, without damage to the other components or to the printed wire board.
2. Description of the Prior Art
The idea of using a boiling solvent in some way to facilitate removal and resolder of electronic components was suggested by E.G. Dingman. See IBM Technical Disclosure Bulletin Volume 13, No. 3 dated August, 1970.
U.S. Pat. No. 4,561,586 to Abel et al. issued some 15 years later describing a method of removing an integrated circuit package soldered to a printed circuit board by flowing a heated liquid over the package.
U.S. Pat. No. 4,762,264 to Peck describes a structure using a preheat portion before passing a board with a surface mounted component through a reflow temperature portion.
U.S. Pat. No. 4,799,617 to Friedman describes a heated gas system for removing surface mounted assemblies from a work piece.
U.S. Pat. No. 4,828,162 to Donner et al. describes a structure using heated jaws for gripping and removing an integrated circuit while leaving other components undisturbed.
Notwithstanding the noble efforts of these specialized structural arrangements to overcome the several disadvantages that are inherent in a hot gas system of component removal, industry returns repeatedly to the hot gas system, only because it remains, until the present invention, the most practical means to accomplish the task.
Therefore, it is still a problem to remove a selected component from a substrate without disturbing other components and adjacent parts.